Technical Field
The present subject matter relates generally to semiconductor memory devices. More specifically, the present subject matter relates to memory devices having a three-dimensional design.
Background Art
Semiconductor memory devices can include blocks of memory cells in a larger integrated circuit or stand-alone integrated circuits. While traditional memory devices build the cells in a two dimensional array, some devices may build a three dimensional array of cells. In some three dimensional flash memories, a NAND string may be built vertically, stacking the individual field-effect transistors (FETs) of the string on top of each other, so that the string extends out from the substrate. Such architectures may provide for very high bit densities in a flash memory device.
Support circuitry, such as line drivers, sense amplifiers, address decoders and other such circuitry may still be built using more traditional layout techniques using areas of the substrate that are not covered by the memory array. While the support circuitry may have multiple layers of material, such as doped silicon, polysilicon, metal, silicon-oxide, or other materials, such designs may still be referred to as having a two-dimensional layout, as they generally do not have active devices stacked on top of each other, like the three-dimensional memory array.